The assignee of applicant has for several decades operated extensively in the art of diaphragm valves, for example for water systems. The main valve shown in U.S. Pat. No. 3,669,143 is of a type which has long been, and still is, manufactured and sold by such assignee. This valve has a relatively high cost in that it has a fully-stabilized diaphragm that does not itself engage any valve seat. Instead, the valve seat is engaged by a separate poppet element associated with the diaphragm. Because the diaphragm and its associated poppet are fully stabilized, against any tilting or flexing or misalignment, the poppet tends to open simultaneously about the full 360-degree circumference of the valve seat.
In an attempt to reduce costs and employ the diaphragm itself as the element which seats on the valve seat, there was developed at the assignee of applicant a valve shown in Pat. No. 4,181,151. This valve was characterized by a diaphragm supporting element having notches, grooves, or holes therein over which the diaphragm seated and through which the water flowed when the valve was partially or fully open. Such an element is relatively expensive to manufacture even if injection molded of synthetic resin, one reason being that the dies for the injection molding are expensive. Furthermore, because of the flowing of water through notches, ports, etc., there was a certain amount of constriction which reduced flow through the valve in the full-open condition. The valve shown in U.S. Pat. No. 4,181,151 has to date been employed only to a limited extent.
There is a strong need for a valve which can be manufactured at low cost and in relatively large volume, yet which has very excellent operating characteristics in numerous types of pilot-operated applications. These include, among others, pressure-reducing or regulating operation, on-off operation, and flow-modulating operation. Some of the necessary characteristics are full shut-off, low noise even at high pressure differentials and low-flow conditions, and high flow capability when necessary.